Electrical generator

ABSTRACT

HEAT SHIELD WHICH PREVENTS HEAT FROM RADIATING FROM THE SOURCE (HOT JUNCTION) TO THE CONTAINER (COLD JUNCTION) AND ALSO MAINTAINS THE VACUUM WITHIN THE CONTAINER. THE WALL OF THE CONTAINER IS COMPOSED OF TITANIUM WHICH IS COMPATIBLE WITH HUMAN TISSUE AND IS REJECTED BY THE BODY.   A HEART PACER IS DISCLOSED WHICH HAS A LONG LIFE (10 OR 11 YEARS) AS COMPARED TO PRIOR-ART PACERS (2 OR 3 YEARS). THIS PACER INCLUDES AN EVACUATED CONTAINER WITHIN WHICH THERE IS A LONG-LIFE RADIOACTIVE HEAT SOURCE. A THERMOELECTRIC TAPE IS WRAPPED AROUND THE SOURCE AND HAS ITS HOT JUNCTION AT THE SOURCE AND ITS COLD JUNCTION AT THE WALL OF THE CONTAINER. THE TAPE INCLUDES A GETTERING

March 14, 1972 D. 1.. PURDY ELECTRICAL GENERATOR 4 Sheets-Sheet 1 Original Filed June 2, 1966 FUEL CAPSULE March 14, 1972 D. PURDY ELECTRICAL GENERATOR 4 Sheets-Sheet 2 Original Filed June 2, 1966 4 Sheets-Sheet 3 mvm D. L. PURDY ELECTRICAL GENERATOR arch 14, 1972 Original Filed June :3,

March 14, 1972 D. L. PURDY ELECTRICAL GENERATOR 4 Sheets-Sheet 4 Original Pi led June 2, 1966 FIG.8

FIG.6

m MlINllilIlilllllllllllillllllllllllllillllmllllll' FIG.I4A FIG. I4B

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FIGJZ United States Patent T ABSTRACT OF THE DISCLOSURE A heart pacer is disclosed which has a long life (10 or 11 years) as compared to prior-art pacers (2 or 3 years). This pacer includes an evacuated container within' which there is a long-life radioactive heat source. A thermoelectric tapeiis wrapped around the source and has its hot junction at the source and its cold junction at the wall of thecontainer. The tape includes a gettering heat shield which prevents heat from radiating from the source (hot junction) to the container (cold junction) and also; maintains the vacuum within the container. The wall of the containeris composed'of titanium which is compatible with human tissue and is not rejected by the body.

places'where no other sources than such generators are available. Among the devices for which such a generator can serveas a power'supply are cardiac pacemakers or heart pa'cers.

A heart pacer supplies electrical pulses to the heart of a patient or subject to 'drive the pumping muscles of the heart. The pacer includes a pulse generator embedded below the abdomen of a subject and an electrode in driving engagementwith the heart. The electrode is connected to the generator through a cable. The cathode pole ofthe pulse supply is at the electrode; the anode pole in the generator. Each pulse is typically a square-wave pulse having a duration of about 1.5 milliseconds. Typically the pulse current is between 4 and 10 milliamperes; the load supplied by the pulses is 300 to 700 ohms paralleled by a capacitance of".25 microfarads and resistance of 1000 ohms. The'frequency of the pulses depends on the subject and typically is 70 plus or minus 5 per minute for humans and 120' plusor minus 5 per minute for dogs. The generator should deliver a: voltage of about 6 volts. The installation of a-pacer in a subject demands major surgery.

[In pacemakers in accordance with the teachings of the prior art the supply is a battery of long-life cells, such as mercury cells. But the life of sucha battery is at most two or-th'ree years and in thelightof the danger to the subject of loss of; battery power and the surgery required to replace batteries a-much longer-life power supply is required. It is an object of this invention to provide a generator which "shall maintain voltage for many years for'supplying electrical power'to heart pacers and the like.

In,-thepractice of-this invention a generator is pro vided whichderivesits primary power from radioactivity. The word radioactivity is here used in its broad sense and may include-alpha ray emitters alone or emitters of alpha, beta-and/or gamma rays.*This generator includes a radioactive material having along half-life and a thermo-electricheat to-electricity,converter.

I [The material develops heat which serves as the hotjunction .for a thermo-electric converter which is constructed to deliver adequate voltage. A suitable radioac- Such a generator should meet the following conditions:

(1) Maximum operational reliability within reason.

(2) Minimum hazard to the patient from radiation.

(3) Maximum freedom for patient from possible adverse physiological efiects.

(4) Dissemination of Pu-328 under any credible hazard must be precluded.

(5) Complete operational stability with no degradation of performance other than that from decay of radioactive material.

(6) Maximum adaptability to surgical demands including particularly ruggedness, ease of manipulation and small dimensions.

(7) Sufiiciently rugged construction to assure more than adequate resistance to shock and vibration under all credible conditions of shipment, implantation and operation.

(8) Sufficient power-excess capability for improved and more reliable circuitry which may require additional power.

(9) Sufiicient inherent power attenuation to preclude injury by reason' of excess power and at the same time adequate voltage.

(10) Structural and functional relationship will enable the minimization of development time and cost, the maximization of time available for in vivo testing and the elimination of the necessity for the solution of peripheral prob lems which would detract from attack of the main construction and testing problems.

(11) Structure inexpensive to manufacture so as to minimize cost and enable large scale utilization.

It is an object of this invention to provide a generator which shall meet the above requirements.

In accordance with this invention a generator is provided which includes a central radioactive fuel capsule about which is wound spirally, tape having embedded therein strands of thermocouple material. Radiation foil insulation is wound between the layers of the tape. Typically, the tape may be formed by spinning thermal insulating thread, for example quartz thread, as woof on the thermoelectric strands as warp. The thread may be the warp and the thermoelectric strands the woof but this has the disadvantage that the relatively stifi metal strands must be turned under and over the yieldable quartz thread rather than the converse. Alternate thermoelectric strands are of opposite polarity materials and the ends of adjacent strands are conductively joined so that the oppositepolarity strands of the tape form a thermopile of long thermocouples in series.

The tape is wound so that the ends of the thermoelectric strand on the inside of the spiral are contiguous to the capsule and form the hot-junction of the pile. The ends of the tape on the outside of the spiral form the coldjunction.

The generator according to this invention has the lowing advantages:

(1) Optimum ratio of thermocouple length to diameter; the thermal conduction path is then long assuring maximum temperature difference, at the same time there is adequate internal power attenuation not subject to short-circuits.

(2) Ruggedness and capability of resistance to shock.

. (3) Minimum space geometry; that is, small dimen- 810118.

(4) Adaptability to large scale mechanized production and testing.

Typically, Cupron Special and Tophel Special thermocouple strands may be included in the tape and they may be connected in parallel redundancy for optimum reliability. Cupron Special is a 'copper-nickel-manganese alloy, typically 59.5% Cu, 40% Ni, .5 Mn; Toph'el Special is a copper-nickel alloy typicaly Cu, 10%" Ni.

fol-

The strands spiral from the central fuel source and occupy the space between the radiation foil vacuum insulation. The thermocouples are attached to the capsule at one end and the heat rejection sink which is the container exterior at the other. The thermocouples are woven as the lengthwise fibers into quartz cloth and are electrically insulated from each other by the laterally woven quartz fibers. This construction combines excellent insulating properties with shock and vibration support. Typically, an external case of titanium, selected for its inertness to body fluids as well as its favorable strengthto-weight ratio, hermetically encloses the bundle formed by the central fuel core and the spirally wound thermocouple ribbons with their interleaved radiation shields. In making the generator the case with its contents is sealed by electron-beam welding in a high vacuum. The power leads are brought, typically, through alumina ceramic-tometal seals into another hermetically sealed chamber containing the heart pacer pulser. Another ceramic-tometal seal conducts the signal to a terminal sealed in clear epoxy. This epoxy is transparent so that the surgeon has a clear view to assure the final connection of the heart lead to the terminal.

All components of the generator made in the practice of this invention are ceramic or metal. To avoid degradat-ion of the vacuum, organic materials are not used within the titanium envelope. The materials from which the radiation shields are made are self-gettering and the vacuum, rather than to degrade, improves over the life of the unit. Connections are made with high conductivity copper conductor straps, as well as extremely low-heat fluxes to minimize the temperature gradients. Typically a generator according to this invention with the pulser can be constructed to fit within a 2.8 x x 6 centimeter envelope.

For a better understanding of this invention, both as to its organization and as to its method of operation, together with additional objects and advantages thereof, reference is made to the following description, taken in connection with the drawings, in which:

FIG. 1 is a view in transverse section of a heart pacer according to this invention;

FIG. 2 is a view in section taken along line IIII of FIG. 1;

FIG. 3 is a view in section taken along line IH-IH of FIG. 2;

FIG. 4 is a view in section taken along line IV-IV of FIG. 1;

FIG. 5 is an enlarged view of the portion of FIG. 1 encircled by circle V;

6 is a plan view of the tape of the apparatus shown in FIGS. 1 through 5;

FIG. 7 is a view in end elevation of this tape;

FIG. 8 is an enlarged view in section taken along line VIII-VIII of FIG. 6;

FIG. 9 is an enlarged diagrammatic view of the tape showing how the thermoelectric strands are connected;

FIG. 10 is a plan view enlarged of an end tab to which the thermoelectric strands are connected;

FIG. 11 is a view in side elevation enlarged of this end tab;

FIG. 12 is a view in end elevation enlarged of this end tab;

FIGS. 13A and 13B are plan views enlarged of a single groove of an end tab showing how the ends of the thermoelectric strands are connected in the grooves of the end tabs; I

FIGS. 14A and 14B are views in end elevation of the structures shown in FIGS. 13A and 13B; and "j FIG. 15 is a schematic of apparatus according to this invention.

The apparatus shown in the drawings includes a Fuel Capsule, Tape wound in spirals about the Fuel Capsule, a. Capsule Support Spider, a Pulser and an Output Cable. The Fuel Capsule, Tape, and Spider are in a container .4 formed by welding two cup-shaped halves 18 and 20 together.

The Capsule includes a plurality of radioactive units 21, 23, 25. Each unit includes an inner tube or sheath 27 within which there is a wire or bar 2'9 of radioactive material. The inner tube is enclosed within a middle tube or sheath 31. The tubes 31 are disposed in the partitions 33 of an outer can 35. Each of the tubes 27 and 31 and the partitions 33 are sealed to a plug 37, 39 (FIG. 2) respectively welded to the associated tube.

Typically the fuel wire consists of standard purity plutonium 238 metal in the form of a small extruded wire approximately 1 inch long and about 0.022 inch in diameter in each of three cylindrical capsule liners or tubes 27. The inner or primary tube 27 is made of Ta-lOW 1 alloy and is capable of containing the pressure of the helium generated by the Pu 238 under the most severe credible accidents. The cylinder wall of each tube 27 is 0.030 inch thick and the end plug is 0.060 inch thick. Approximately 400% void volume is provided in the capsule to allow for ease of assembly and fuel form flexibility. The available data on materials compatibility indicate that there is no likelihood of damage from lack of compatibility of Ta- 10W with Pu metal under the anticipated conditions of operation for the life of the generator. There is sound reason to believe that the generator would be safe under all credible thermal excursions including that caused by a high octane gasoline fire (1300 C.) for periods up to five hours. Additional safety can be achieved by available flexibility which allows for use, in alternative practice of this invention, of a Zr-Pu fuel alloy or an additional encapsulation of Zr or Hf that would delay the dissolution attack of the container by forming a high melting point alloy with the plutonium at the interface. j

The Ta-lOW tube 27 is protected from high-temperature oxidation by the Hastelloy C tube or sheath 31. Hastelloy C is selected because it has resistance to the corrosive effects of abroad spectrum of chemical reagents as well as resistance to oxidation at high temperatures. The Hastelloy sheath is 0.009 in. thick with 0.060 end plugs. Addition corrosion protection is obtained by a 0.001 inch coating of Pt over the Hastelloy which is pro vided to prevent reactions with the Ti outer can 35 dur ing possible thermal excursions.

The three individual tubes 31 are contained in the outer can 35 of Ti to fix them in the required position and to facilitate the joining of the thermocouples to the heat source. Titanium is selected. for ease and reliability of joining, high strength weight ratio, and because it has unique resistance to a broad spectrum of chemical reagents in which accidental immersion may be postulated. The use of Ti-0.2 Pd alloy, in alternative practice of this invention, allows the broadening of this spectrum to cover reducing reagents as well as oxidizing reagents.

The tube 27 is filled with helium or argon or other inert gas at about one atmosphere pressure and then the plug 37 is welded to its rim by electron-beam or tungstenarc welding. The helium provides the thermal conductivity between the wire 29 and the Ta-IOW wall- The tube 31 and the partitions 33 are evacuated and the plugs 39.and 41 sealed to their rims by electron-beam welding.

Alternative Fuel Capsules in the practice of this invention may include Pu02 as fuel. In addition platinum may replace the Hastelloy C alloy for the tube 31 where higher absorption of gamma rays is demanded.

The Fuel Capsule is supported by a Capsule Support Spider at each end. Each Spider (FIGS.. 2 and 3) includes a T-plate or bracket 51, whose web 53 and cross member 55, have holes to reduce weight. Each web 53 has a wire support pin 57 at its end. and the cross member 55 has like pins 59 and 61 at its ends. Capsule-support 1 For brevity alloys are herein "described -In abbreviated form. The first chemical symbol describes the major component and the numbers before subsequent symbols the content of these components. Ta-10W is an alloy of tantalum-tungsten with Ta and 10% W.

wires 63, 65, and 67, diverging from a center plate 68 (FIG. 2) to which they are secured at points that are about equally'sp aced, pass over the pins 57, 59 and 61 respectively and through spring tabs 69, 71 and 73 and are secured in grooves 75, 77,79 respectively. The spring tabs 69, 71, 73 tension the wires'63, 65, 67. The tabs 69, 71, '73 are included to provide necessary damping and spring action against dynamic motion of the Fuel Capsule relative to the insulation and thermoelectric parts insuring impact and vibration protection. The cross members 55 of the T -plates 51 are each bolted to an angle 81 (FIG. 2) secured to the outside wall 83 of the generator. The plates'68 are secured to the ends of the Fuel Capsule.

Typically the T-plate 51 and the wires 63, 65, 67 may be composed of Ti-6Al-4V alloy. The wires 63, 65, 67 are of .005 inch diameter. The wires have an annealed tensile strength of about 130,000 pounds per square inch and are adequate to constrain the motion of the capsule. In addition tothe mechanical considerations, the Ti-6Al- 4V alloy is chosen for its low thermal conductivity in comparison with other high tensile strength wires. This assures a low heat loss through these wires.

The'heat developed by the Fuel Capsule is converted into electricity by a thermoelectric pile embedded in the Tape. The thermoelectric pile includes a plurality of thermocouples 89 (FIG. 9) each composed of a pair of dif ferent wires 91 and 93 one electrically negative, or having excessive electrons, designated N and the other having excessive holes, designated P. The wires are connected at their ends in parallel in double, pairs (FIGS. 8 and 9) to form hot junctions 92 at the Fuel Capsule and cold junctions, 94 on the outside of the Tape. Typically, the

I wires 91 maybe of CUPRON alloy and the wires 93 of Tophel alloy.

The Tape is composite and is made up of six layers (FIG. 8). There is a heat radiation reflecting layer 95 typically composed of Titanium-Zirconium foil. There are two layers 97 and 99 of thermoelectric cloth in which the-wires 91 and 93 form the Warp and electrical and .thermalinsulating threads 101 and 103, typically quartz 97, the .layer97 and the layer 99, and the layer 99 and the reflecting layer 95 of the adjacent turn of Tape. The thermal radiation shield 95 of each layer of Tape extend beyond the thermoelectric cloth layers 101 and 103 and the insulating cloth layers 107, 109 and 111.

Each Tape includes a pair of ceramic connection tabs 12 1 and 123 (FIGS. 6, 9, 13A, 13B, 14A, 14B) one for the hot junction 92and the other for the cold junction 94.

The tabs 121 and 123 may be composed of a material such as "alumina which is thermally conducting but electrically insulating. Each tab has a plurality of grooves 125 which are coated with a brazing compound 127, typically copper-silver. The layers 129 and 131 of copper and silver may be deposited on a titanium layer 133 FIG. 14A) by evaporation or electroplating; the titanium is deposited by evaporation or fusion. The ends of the thermocouple wires 91 and 93 extend freely from the thermocouple cloth. The junctions -92 and '94j=a'r'e formedfor eac'h Tape by placing the ends in the grooves 125 coated with the layers'129, 131, 133 and heating the'entire unit including the Tape and tabs 121 and 123 to. the eutectic temperature of the brazing compound 127 which. for copper-silver is 790 C. The compound 127 fuzes around the ends of the wires 91 and 93 (FIGS..13B,14B).

I Inyiew of the manner a. which the wires 91 and 93 are wove'n into the cloth 97, 99 the proper placement of tli'eyvires' the required groove 12 7 naturaland presents no problem. The bottom of the alumina ceramic tabs 121 and 123 are brazed to thin tabs 141 and 143 of copper (FIGS. 1, 6, 9, 11, 12) which are then spot-brazed to a copper strap 145 (FIGS. 1, 2, 3, 5) which is later connected to the fuel capsule and to the external surface respectively of the generator. The copper tabs 141 and 143 are bent to compensate for thermal expansion and manufacturing tolerances which stress the Tape. The copper tabs 143 to which the ceramic is attached at the cold junctions 94 have small convolutions 147 (FIG. 1) to accommodate relative length changes in the tape during manufacturing and operations. This technique allows the ceramic 123 to essentially float with a thin copper piece which cannot stress it. The copper-silver eutectic does not wet the surface of the ceramic 121 or 123 and does not short out the junctions 92 or 94 by flowing over from junction to junction. It only wets the titanium 133 (FIG. 14A) and the thermocouple wires 91 and 93.

A plurality of Tapes 151, 153, 155, 157, 159, 161, 163 (FIG. 1) are wound spirally from a hot position contiguous to the Fuel Capsule to a position contiguous to the external container wall 83 of the generator. Each tape has ceramic terminals 121 and 123 on each side. The hotjunction ceramics 121 of the Tapes 151 through 163 are distributed around the periphery of the Fuel Capsule and the cold-junction ceramics 123 are distributed (spaced) along a portion of the half wall 18. The Tapes 151 to 163 start from positions spaced around the periphery of the Fuel Capsule and terminate at positions spaced along the inside of Wall 83 and are interwound. The overlapping ends of the radiation-shields 95 of the tapes form a generally frusto-conical internal surface terminating at the wires 63 of the Capsule Support Spider. The interior of this surface is filled with sheets 171 of the titaniumzirconium thermal-radiation reflecting foil.

The hot junctions -92 of the Tape are connected in thermal interchange relationship with the Capsule through the copper strap which is brazed to the Fuel Capsule. The cold junctions 94 are connected thermally to the wall 83 which is brazed to a connecting strap 173, in turn brazed to outer strap 145, in turn brazed to flexible connector or tab 143. The cold junction 94 of the end couple 175 (FIG. 15) on one side of the ceramic 123 connected to Tape 163 is electrically grounded to the wall 83. The cold junction of the end couple 177 on the opposite side is electrically connected to the cold junction of the adjacent end couple of the succeeding tape 161 through a strap 179 and the cold junction on the opposite side is likewise connected to the adjacent end couple of the next Tape 159 and so on, each strap 179 connecting the couples of a Tape, in series with the couples of the others. The cold junction of the end couple 181 of Tape 151 is connected to the output conductor 183 (FIG. 1) from the generator. Typically each tape 151 through 163 has 424 thermocouple wires; these are connected to form 106 hot junctions and 107 cold junctions.

To assemble the generator the tapes 151 to 163 and the copper straps 145 are placed in a fixture which supports the tapes in the proper orientation with respect to the copper straps at both ends of the tapes. The copper tabs 141 and 143, which have been pre-attached to the ceramic tabs 121 and 123 to which the thermocouple ends have brazed, are joined to the copper heat transfer straps 145 located at both ends of the thermocouple tapes 151 through 163 by spot brazing with Cu-Ag alloy. The eight tapes are thereby combined into a single unified thermocouple assembly of the proper length and dimensions which can be entirely pretested before going on to the next step of assembly. The next step consists in attaching the tensile support wires 63, 65, 67 to the Fuel Capsule, placing the end thermal insulation 171 between the three support wires at each end, and affixing the tensile support wires to the supoprt T-brackets 51 which have. been prefixed to an assembly fixture. The assembly fixture is constructed so that the brackets '51 are held at the proper separation for insertion and fastening into the case 83. 500 milliseconds. The pulses have an amplitude of 6 Care is taken to exert appropriate tension on the wires milliamperes. The steady-state conduction of the device when they are fastened to the bracket. The insulation 171 is about 3 microamperes. (FIG. 2) is positioned within the tensile wires 63, 65, 67 The pulsing device has only one input terminal conand the fixture can be rotated about an axis passing 5 nected through a ceramic-to-metal feed through conthrough the center of the Fuel Capsule. Next the hot-juncnector 204 (FIG. 2), a conductor 205 and another cetion end of the copper terminal thermocouple strap 145 ramic-to-metal feed-through connector 207, sealed through is attached around the Fuel Capsule by first positioning the half 18 of the container, to the conductor 183. The the end of the terminal strap 145 into the groove provided conductor 183 impresses about 6 volts negative on this in the Fuel Capsule and spot brazing the strap to the 10 input terminal. The opposite terminal of the pulser is Capsule. The cold junction thermal joint is then atgrounded to the same ground as the grounded terminal tached to the copper strap 173 provided in half 18 of the of the thermopile. The pulsing device includes an output container. This joint is made by spot brazing the ends of conductor 221 (FIG. 4) extending out of the container the copper straps 173 together with copper-silver eutectic 201 and connected to a connector ring 223 to which it alloy. The Fuel Capsule which is still affixed to its windtransmits the pulses produced. ing fixture is now rotated around its axis until the thermo- The pulser is molded in a generally rectangular mass couple tape assembly 151 through 163 is wound around 225 of transparent epoxy resin. The conductor 221 is the central axis, and the spider is then fastened to the embedded in this mass. The mass 225 includes a tubular brackets provided in the interior of the container. The opening 227 intermediate whose ends the ring 223 is hermetic lead 183 which is a thin flat strap, is attached to 20 moulded. The opening 227 tapers slightly from both of the electrical terminal on the thermocouple assembly, its ends towards the ring 223. thus completing the electrical connection. The output cable includes a coiled conductor 231 typi- The unit, exclusive of the Pulser, is now placed in a cally of ELIGLOY alloy. The conductor 231 is enclosed high vacuum outgassing device and a vacuum provided in a flexible tube 233 preferably of silicon rubber which where it will be outgassed at a temperature of 500 C. is enclosed in an insulating sheath 235 typically of siliuntil the pressure in the system is reduced to 10- millicone rubber. A stud 237 having a generally frusto-conical meters of mercury. This drives oif any residual water center portion 239 from which a screw 241 extends is vapor, adsorbed gas or other contaminants which could, secured in the end of the sheath 235. The conductor 231 over the anticipated 10 year life, degrade the system and is connected to the attenuated end 238 of the stud 237. cause generator failure. The vacuum is broken with pure, The output cable also includes a connector nut 243. This dry argon after which the half 20 of the container is nut 243 is slotted at one end 245 and carries an internal placed over the half 18. The assembled unit is then placed thread 247 at the other. There is. a neck between the in a chill block fixture, evacuated to 10- mm. of Hg, and ends 245 and 247 on which an O ring 249 is mounted.

electron-beam welded. This procedure ensures cleanliness By turning the slotted head 245, the screw 241, frustoand freedom from degrading contaminants which, as inconical portion 239, sheath 235 and the parts attached to dicated above, may adversely affect the operation of the it are pulled towards the ring 223 in one direction and the system over its lifetime. nut 243 and O ring 249 are pulled in the opposite direc- The Pulser includes a hermetically sealed casing 201 tion. The ring 223 has a tapered inner surface which is mounted on the half 18 of the container adjacent to the engaged in firm electrical contact by the portion 239. The

point where the conductor 183 extends from the hot O ring seals the tapered hole 227 on one side and pro electrical terminal of the thermopile. Within the container jections 251 on the outside of the sheath 235 seal the 183 there is a pulse producing device 203 including solid hole on the other side.

state valves or transistors. Typically the pulse producing In the use of this apparatus the power generated by device may be a free-running multivibrator with its imthe thermopile energizes the pulser which supplies pulses pedances set to produce the pulses of the desired durato actuate the heart.

tion having the desired amplitudes and the desired on Table Ibelow shows the principal components included and oil times. In a typical situation the pulse producer in the apparatus in accordance with this invention and produces pulses of 2 millisecond duration at intervals of the reasons for their selection:

TABLE I Item Description Reason for selection Fuel (preferred) Pu-238 metal Wire Low surface radiation level. High energy density. Easily manufactured and shaped. Low manufacturing costs. (Alternate-1) P1102 micrcsphcles Reasonable surface radiation levels for age groups representing vast ma ority of users. Highly inert.

(Alternate-2)... Pu -238 metal of special purity. Extra low surface radiation level. Capsule geometry Triple capsule Low surface dose rate. Minimum thickness. Maximum strength. Primary fuel capsule (inner Tantalum-10% tungsten alloy Excellent compatibility with fuels. High strength at elevated temperatures to unit 21). contain helium pressure. Second fuel capsule (Middle Hastelioy 0" High temperature oxidation resistance. Resistance to corrosion attack by insheath 31). dltllstrial chemicals. Excellent high temperature compatibility with tantalum a oys. Reaction harder Platinum Prevention of the development of low melting point phasesbetween Hastelloy C and titanium. Excellent high temperature oxidation resistance. Excellent resistance to chemical attack. Third fuel capsule (Outer Titanium-0.2% palladium alloy Corrosion resistance to a broad range of chemical reagents. Ease of joining can 35). thermocouples. Excellent oxidation resistance. Thermocouple geometry Spiral wind Ease of integration into insulation. Maximum diameter wire in small volume.

High reliability. Provides for long length thus allowing greater diameter in a minimum of space. Allows for an all cerarnic to metal system with high reliability. High surface area brazed joints allow for complete open assembly fixturing. Ease of manufacture and test.

Thermocouple material Cupron special-'loplicl special. Ease of brazing and joining. Best figure of merit ,of state-of-the-art thermopile materials having good mechanical properties." Stability of metallurgical, mechanical compositional and electrical properties. Readily available in desired wire diameters. Good mechanical properties. High reliability. Large g I L/A possible. No DC to DC converter required.

Thermal radiation insulation- Vacuum, titaniummrrconlum radia- High performance. Minimum thermal loss. Easily integrated into spiral wind.-

tion shields with spiral wind. Self gettcring of vacuum in case. r

Elcctricallnsulation Quartz cloth, spiral wind... Can be woven with thermocouple wires for low cost assembly in production.-

Spaces thermocouples for ease of assembly. Supports and cushions thermocouple wires. Can be outgassed at high temperatures. Separates irradiation shields. Stable operation in vacuum.

TABLE I.Con tinued Item v Description Reason for selection Outer case and anode Titanium Excellent compatibility with human tissue. Electrochemically inert. Corrosion resistance to body fluids. Good ductility and strength. Low density allows thicker, more reliable case. Excellent weldability when protected from the atmosphere. Good formability. Good bond strength to epoxy. Essentially pure material minimizes chances of metallurgical defects. Electron-beam welding Ease of Weld fixturlng. Small heat applied zone. Vacuum seal ofi at time of weld. Clearepoxy Excellent history of compatibihty in body. Transparency allows surgeon to see final connection being made thereby assuring implantation reliability. Resistant to water swelling. Provides resilient mounting of electronic components and connections. May be autoclaved. Excellent joining to titanium.

Case closure method .Potting compound-.-

Electrical lead Coiled Elgiloy alloy High streng h-coil provides resiliency. High reliability bond on extended liit j I test. Excellent corrosion resistance. Excellent history of compatibility in body. Lead insulation Silicon rubber Excellent res liency. Excellent history of compatibility in body. Excellent I electrical insulation. May be autoclaved, Wide range of service temperatures. Resistant to water swelling. Electrodes Cathode Chardack electrode with Successful operating use. 50 cm. spiral Elgiloy electrode wire. Generator interior Vacuum Allows for minimum thermal loss. Allows for maximum life. Avoids gas pressure environment. flfl f 7 build up and leaks. Provides ultraclean environment to prevent degradation: Hot junction temperature-.. 200 C- Proi zid es i mnimum of fuel loading at maximum efliciency point. Long life. High re la 1 y Thermocouple 'oin'ing Brazed ceramic High rehability. Ease of assembly. Large surface area, low resistivity joint. All

ceramics and metal. Utilizes state-of-the-art brazes. Automatically interconnects circuit. Ease of check out. High shock resistant construction. Reinforced 4 ceramic structure. Cushioned thermal connectors. Capsule support Tensile wire (63, 65, 67) High Strength, Minimum thermal loss. Cushioned impact. Ease of assembly. I i Supports radiation shields. Easily joins to wall of capsule. High vibration and shock resistance. Thermal connections Brazedjoints Maxim m r l b l y. implicity of assembly. Excellent heat transfer. Hivh i temp. outgassing capability.

Typically, stem pacer according to this invention has 4. The generator of claim 1 wherein the web is a woven the properties outlined in the. following Table II. tape composed of sets of warp threads and woof threads,

TABLE H one of said sets being of thermally and electrically insulating material and the other of said sets being the alterulse here to isti s: P (a; ourien tufnr 4m milliarnperes into 300 to 100 ohms 3() Hate Posmve and negatlve elementsparalleledt by .25 microfai'ad and 1,000 5. The generator of claim 1 wherein the heat source is ohm resis or. (1 Shape 1.5 millisecond duration rectangular df s l q Web Serves to absorb the pulse. re re ion rom sai ma eria Rate: (c) 1. H ma 70 plllls or minus 5 per llillllillllltt. g'tg ginerator i 2 1 Wherem t i of heat 2. Animal 120p us or minus 5per u e. an e We are cnc ose in an evacua e con ainer. rsu l 9 ggg Metallic couples of Tophel Special and The generator f l im 3 wherein he urce of heat t i S Ciuprori lpilacial Alloys. and the web are enclosed in an evacuated container and b 0 cu wherein the thermal-radiation refiectin material is also F 1 Plutonium 23s metal. g T i iial poviveii output 162 microwatts. a gettering material. Ove all haracter st cs:

f gm 6 x 5 x 2.8 centimeters. No radius smaller t'af eIi F F f qg t q an i f lg than .5 centime ers. con 1n a ea source in sai con ainer, a ea sin i ht 97.5 ams.

(b) sl' iecific gravity 1.4 (an be decrliieased with dfcreasetin j g i s: qd g t i l il defiterzdmg between weight efiecte by remova 0 ex ra Sal ea source an 83.1 ea Sin an ea -ra 1a 1011 reinsulating tapes).

(0) External radiation Betwee? 1.5 and 25 mrem/hr. on surface fig gil g cg s ggtigf g i 'f i mtcarlirsl be 0 sys em. i c P so in m eria an mg 0 amg ggg Spiral Elguoy alloy win, tain the vacuum within said container.

Anode Titanium (Electrochemically Noble 9. An apparatus for insertion in the human body by a (e) Operatingmeflme: metal) 3161 SS can also be used surgical operation including a thermoelectric generator Human 10 years objective20 probable. having an evacuated container of a material not re ected Animal syearsmmimum. by animal body, a heat source 1n sa1d container, a heat Environmental conditions: sink, thermoelectric means in said container extending (5) P 353 35; F 974% between said heat source and said heat sink, and heat-radi- 2. surracefi'r 109. in 1d ti ation reflecting means in said container, said reflecting (b) Interface 1 32; i ilz Y means being composed of a getterrng material and humi y 3 it d o to serving to maintain the vacuum within said container,

(c) y more an a Y p whereby deterioration of the power of said enerator regraphite surface can be tolerated. g

(d) Vibration Minute man missile sp c a quiring a surgical operation for rcmsertion of a replacement generator are substantially precluded. What is claimed is: 10. A generator of electrical power including a source A generator of electrical P lilcilldlng Source of heat, a web of thermally and electrically insulating ma- Of heat, a Web of thermally f a lf lnslliatlng terial having alternate positive and negative thermoelecterlal havlng alternate Posltlve and negative thermoelgc' tric elements embedded therein longitudinally thereof, said tric elements embedded therein longitudinally thereof Wound around said source in layers from an inside position thermally contiguous to said source to an outside position thermally remote from said source, the ends of said elements respectively at said inside position and at said outside position being electrically joined to form hot and cold junctions respectively, and means connected to one web being so disposed adjacent said source in layers from an inside position thermally contiguous to said source to an outside position thermally remote from said source,

that heat emanating radially from said source is transvcrsely intersected by successive segments of said tape, the ends of said elements respectively at said inside posiof Said junctions to derive electrical Power from said tion and at said outside position being electrically joined elements to form hot and cold junctions respectively, and means 2 generator f claim 1 wherein the means to connected to one of said junctions to derive electrical rive electrical power is connected to the cold junction. Power from 831d eiements- 3. The generator of claim 1 wherein a layer of thermal- 11. The generator of Claim 10 Whefeln the m ans t radiation reflecting material is interposed between successive layers of the web.

derive electrical power is connected to the cold junction.

12. The generator of claim 11 wherein a layer of ther- 1 1 mal-radiation reflecting material is interposed between successive layers of the web.

13. The generator of claim 11 wherein the heat source is of radioactive material and the web serves to absorb the radiation from said material.

14. The generator of claim 11 wherein the source of heat and the web are enclosed in an evacuated container.

15. The generator recited in claim 10 wherein is included casing means surrounding said source and associated means; and upper and lower wire suspension means adapted to couple said source of heat to be suspended from said surrounding casing means in a mechanically stable, thermally insulative suspension arrangement; each suspension means comprising at least two fine wire connections.

16. A thermoelectric generator including an evacuated container, at least one thermoelectric element in said container connected to form a hot-junction and a cold-junction, and combined heat-radiation, reflecting means including gettering means within said container disposed to suppress the flow of heat by radiation from said hot junction to said cold junction.

17. The combination as recited in claim 16 wherein said radiation refiecting-gettering means comprises at least one shielding layer, said layer including material selected from the class consisting of Zirconium, Titanium and their alloys.

18, The combination as recited in claim 17 wherein said layer is essentially comprised of Zirconium materials.

19. The combination as recited in claim 17 wherein said layer is essentially comprised of Titanium materials.

20. The combination as recited in claim 17 wherein said layer is essentially comprised of Zirconium and Titanium alloy material.

21. The combination as recited in claim 20 wherein said alloy comprises 87.5 Zirconium, the balance Titanium.

22. A thermoelectric generator including an evacuated container, at least one thermoelectric element in said container connected to form a hot-junction and a cold-junction, and combined heat-radiation reflecting means and gettering means within said container disposed to .suppress the flow of heat by radiation from said hot-junction to said cold-junction, said radiation reflecting-gettering means comprising at least one set of stacked foils disposed along a heat-emanatingpath for attenuation of the heat energy travelling along said path, said foils being of a material selected from the class consisting of zirconium and titanium and their alloys. h

References Cited UNITED STATES PATENTS I r 2/1963 Canada 1s 175.s

ALLEN B. CURTIS, Primary Examiner us. 01. X.R.; 136-205, 223, 22s 

